Conventionally the spectacle frame is made integral with the lens frames, and the distance between the opposite lens frames is not variable.
When suitable spectacles are to be prepared, a spectacle frame is selected in accordance with the width of the face first, and the lenses are cut in conformity with the shape of the lens frames. If the lenses are cut so as to be in alignment with the pupils when the distance between the pupils is excessively large or small relative to the width of the face, the lens, if having a small effective diameter, will include in its inward or outward portion a mere glass portion which fails to function as a lens, consequently giving rise to the problem of causing fatigue to the eyes of the wearer.
To overcome this problem, another problem arises in that there is the need to specifically select and cut lenses having a larger effective diameter.